[en] Since the last IAEA meeting, experiments and system modification in the HT-7 tokamak focused on long pulse discharges based on lower hybrid current drive (LHCD) under different scenarios to support the EAST project both physically and technically. The long pulse discharges at the level of Ip 60 kA, ne(0) 0.8-1x10¹⁹/m³ has been extended to longer than 6 minutes using about 150kW of LHCD only, which are the new records of both the pulse length and injected energy in HT-7. A new steady-state AC operation mode has been demonstrated up to 53 s in ohmic plasmas and 30s in LHCD plasmas at the level of Ip=100-125kA, ne(0) 1.5-2.5x10¹⁹/m³. The relevant physics concerning on the lower hybrid current drive efficiency, MHD instability, conversion efficiency of LHW to poloidal energy t and dynamics of runaway electrons were studied. Radial propagation of electrostatic turbulence and intermittently occurring large-scale coherent structures were measured using the Langmuir probe arrays to study the turbulent transport in the plasma peripheral region. (author)

[en] An m/n=1/1 internal mode instability in lower hybrid current driven (LHCD) plasmas. has been observed previously on the HT-7 tokamak [Youwen SUN, et al, Plasma Phys. Control. Fusion 47, (2005) 7451. This mode appears during the sawtooth ramp, saturates, damps and finally disappears before the subsequent sawtooth collapse and before the appearance of the precursor oscillations. It is named 'mid-oscillation' for distinguishing from the precursor oscillation and the post cursor oscillation. It usually does not triggering the sawtooth crash, and its nonlinear evolution quite resembles the resistive tearing mode. The effect of the barely trapped suprathermal electrons may be ignored due to the relatively low threshold LHCD power for exciting the mid-oscillation [Youwen SUN et al, Phys. Plasmas 12, 092507 (2005)l. This mode is most likely destabilized by the current density gradient at the rational surface. Hence, the final stabilization of mid-oscillation before the subsequent sawtooth crash may be caused by the flattening of the local current density profile. It is proposed in this paper that the flattening of the local current density profile is caused by the locally enhanced radial transport of the suprathermal electrons driven by LHCD due to existence of the mid-oscillation. Based on the local transport model [Z. Chang and J. D. Callen, Nucl. Fusion 30, 219 (1990)], it is obtained that the density of the fast electrons will decrease inside the rational surface while increase a little outside it due to the mid-oscillation when the LHCD deposits the rational surface. Therefore, the current density profile will flatten near the rational surface, and the mid-oscillation may become stable again in this condition. This is in agreement with the experimental observation, in which it was found that the mid-oscillation occurred when the LHCD deposited in the central region, and only a precursor oscillation appeared when the deposition location move outwards [Youwen SUN, et al, The 5th General Scientific Assembly of Asia Plasma and Fusion Association, Jeju, Korea, August 29-31, 2005, TO1]. The numerical calculation shows that the time scale of the evolution of the current density profile is also the same order as the characteristic time of the evolution of the observed mid-oscillations. (author)

[en] From magnetic fields in PF coils of EAST expressed as elliptic integrals, the heat load of PF coils during plasma discharge is determined. The maximum temperature rise of these coils is also estimated from the thermo-hydraulic condition of the magnet operation. (authors)

[en] The use of advanced nondestructive testing technology to detect the flow gap of the plate fuel assembly has become an integral part of the production and use of plate fuel components. Domestic and foreign research and published literature on fuel assembly flow gap detection methods show that the main research directions focus on eddy current method. In this paper, the eddy current method is used to study of detecting the flow gap width of the plate fuel assemblies. Based on the eddy current method is established by the special transducer and standard sample of fuel assembly flow gap. The gap detection method realizes the fast and accurate measurement in the full size range of the research reactor fuel assembly. The flow gap width of the fuel assembly in this paper ranges from 1.3 mm to 2.8 mm. Through multi-batch inspection and verification experiments, the detection accuracy is ± 0.02 mm. (authors)

[en] Highlights: • Thermal design requirements for EAST RMP coils are summarized. • Cooling parameters based on both theoretical and numerical solutions are determined. • Compromise between thermal design and structural design is made on number of turns. • Thermo-mechanical calculations are made to validate its structural performance. - Abstract: Resonant magnetic perturbation (RMP) has been proved to be an efficient approach on edge localized modes (ELMs) control, resistive wall mode (RWM) control, and error field correction (EFC), RMP coil system under design in EAST tokamak will realize the above-mentioned multi-functions. This paper focuses on the thermo-mechanical analysis of EAST RMP coil system on the basis of sensitivity analysis, both normal and off-normal working conditions are considered. The most characteristic set of coil system is chosen with a complete modelling by means of three-dimensional (3D) finite element method, thermo-hydraulic and thermal-structural performances are investigated adequately, both locally and globally. The compromise is made between thermal performance and structural design requirements, and the results indicate that the optimized design is feasible and reasonable

[en] Magnetic diagnostics is one of basic measurement systems for Tokamak plasma current and shape control. The accuracy of magnetic data will influence the plasma shape reconstruction. In this paper, the calibration of magnetic diagnostics is carried out on the EAST Tokamak. The overall uncertainties of magnetic sensors are analyzed from the calibration and vacuum shots. The uncertainty results are used as fitting weight in plasma shape reconstruction code (EFIT). Based on EFIT simulation and experiment data fitting results, the sensitivity of the magnetic data uncertainty in the plasma shape reconstruction is analyzed. (author)

[en] The excitation mechanism and stabilization of the observed m/n = 1/1 instability during the sawtooth ramp phase in the lower hybrid current driven plasmas on the HT-7 tokamak (Sun Y et al 2005 Plasma Phys. Control. Fusion 47 745-56) have been investigated in this paper. This mode is most likely destabilized by the current density gradient at the q = 1 surface. Based on the local transport model, it is shown that the saturation and stabilization of the m = 1 mode before the subsequent sawtooth crash may result from the flattening of the current profile because of the locally enhanced transport of the suprathermal electrons due to the magnetic island

[en] The barely trapped suprathermal electrons can destabilize the internal kink mode when their density gradient is positive within the rational surface and the beta value of the suprathermal electrons exceeds a threshold value. With the assumption of two different models of energy distribution of the suprathermal electrons, the threshold beta value of the barely trapped suprathermal electrons, the real frequency, and the growth rate of the internal kink mode are found in this paper. The results are in reasonable agreement with the recent experimental observations on DIII-D tokamak [K. L. Wong, M. S. Chu, T. C. Luce et al., Phys. Rev. Lett. 85, 996 (2000)]

[en] A new oscillation with m = 1 and n = 1, where m and n are the poloidal and toroidal mode numbers, respectively, has been observed with lower hybrid current drive (LHCD) on the HT-7 tokamak. This mode appears during the sawtooth ramp, saturates, damps and finally disappears before the subsequent sawtooth collapse and before the appearance of the precursor oscillations. The necessary condition for its observation is that the sawtooth period exceeds 6-7 ms and that the LHCD power exceeds the threshold value of about 90 kW. We propose that the mode may be destabilized by the current density gradient, the evolution of which is determined by the suprathermal electrons generated by the LHCD

[en] The non-linear interplay between the resistive wall mode (RWM) and the toroidal plasma flow is numerically investigated in a full toroidal geometry, by simultaneously solving the initial value problems for the n = 1 RWM and the n = 0 toroidal force balance equation. Here, n is the toroidal mode number. The neoclassical toroidal viscous torque is identified as the major momentum sink that brakes the toroidal plasma flow during the non-linear evolution of the RWM. This holds for a mode that is initially either unstable or stable. For an initially stable RWM, the braking of the flow, and hence the eventual growth of the mode, depends critically on the initial perturbation amplitude.